In a wireless local area network (WLAN) standard of an 802.11ax (11ax for short) version, an indoor scenario and an outdoor scenario are considered.
In comparison with the indoor scenario, a long distance in the outdoor scenario generates a longer delay spread, which results in severe inter-symbol interference (ISI). To reduce ISI impact, a longer cyclic prefix (CP) is considered and applied to a data section of a transmitted packet structure. In addition, to reduce overheads of the CP, an FFT with a larger quantity of points is used in the data section, that is, a longer symbol period. Using the longer cyclic prefix can reduce inter-symbol interference of a data field section, thereby improving transmission performance.
However, for a signal field, even though a most robust binary phase shift keying (BPSK) modulation method, a lowest ½ bit rate, and a CP length (0.8 μs) in the existing 802.11a/g/n/ac standards are used, a PER requirement for the signal field (1% or lower is required) still cannot be met due to the ISI impact. Therefore, for the outdoor scenario, a more robust signal field needs to be designed.
A signal field in a WLAN system generally includes two parts: a legacy signal field (L-SIG) with a need to consider backward compatibility and a signal field for identifying a new feature, for example, a high throughput signal field (HT-SIG) in 802.11n (11n for short) or a very high throughput signal field (VHT-SIG) in 802.11ac (11ac for short). Similarly, a signal field for identifying a new feature in 11ax is named as a high efficient signal field (HE-SIG).
How to ensure both robustness of packet transmission in an outdoor scenario and backward compatibility is a technical problem that needs to be resolved in the present invention.